Large-Scale Self-Catalyzed Spongelike Silicon Nano-Network-Based 3D Anodes for High-Capacity Lithium-Ion Batteries.

Here, we report on the large-scale one-step preparation, characterization, and application of three-dimensional spongelike silicon alloy composite anodes, based on the catalyst-free growth of porous silicon nanonetworks directly onto highly conductive and flexible open-structure stainless steel current collectors. By the use of a key hydrofluoric-acid-based chemical pretreatment process, the originally noncatalytic stainless steel matrix becomes nanoporous and highly self-catalytic, thus greatly promoting the formation of a silicon spongelike network at unexpectedly low growth temperatures, 380-460 °C. Modulation of this unique chemical pretreatment allows control over the morphology and loading properties of the resulting silicon network. The spongelike silicon network growth is capable of completely filling the openings of the three-dimensional stainless steel substrates, thus allowing full control over the active material loading, while conserving high mechanical and chemical stabilities. Furthermore, extremely high silicon loadings are reached because of the supercatalytic nanoporous nature of the chemically treated stainless steel substrates (0.5-20 mg/cm2). This approach leads to the realization of highly electrically conductive Si-stainless steel composite anodes, due to the formation of silicon-network-to-stainless-steel contact sections composed of highly conductive metal silicide alloys, thus improving the electrical interface and mechanical stability between the silicon active network and the highly conductive metal current collector. More importantly, our one-step cost-effective growth approach allows the large-scale preparation of highly homogeneous ultrathin binder-free anodes, up to 2 m long, using a home-built CVD setup. Finally, we made use of these novel anodes for the assembly of Li-ion batteries exhibiting stable cycle life (cycled for over 500 cycles with <50% capacity loss at 0.1 mA), high gravimetric capacity (>3500 mA h/gSi at 0.1 mA/cm2), low irreversible capacity (<10%), and high Coulombic efficiency (>99.5%). Notably, these Si spongelike composite anodes of novel architecture meet the requirements of lithium batteries for future portable and electric-vehicle applications.

Tissue-like Silicon Nanowires-Based Three-Dimensional Anodes for High-Capacity Lithium Ion Batteries.

Here, we report on the scalable synthesis and characterization of novel architecture three-dimensional (3D) high-capacity amorphous silicon nanowires (SiNWs)-based anodes with focus on studying their electrochemical degradation mechanisms. We achieved an unprecedented combination of remarkable performance characteristics, high loadings of 3-15 mAh/cm(2), a very low irreversible capacity (10% for the 3-4 mAh/cm(2) anodes), current efficiency greater than 99.5%, cycle stability (both in half cells and a LiFePO4 battery), a total capacity of 457 mAh/cm(2) over 204 cycles and fast charge-discharge rates (up to 2.7C at 20 mA/cm(2)). These SiNWs-based binder-free 3D anodes have been cycled for over 200 cycles, exhibiting a stable cycle life. Notably, it was found that the growth of the continuous SEI layer thickness, and its concomitant increase in resistivity, represents the major reason for the observed capacity loss of the SiNWs-based anodes. Importantly, these NWs-based anodes of novel architecture meet the requirements of lithium batteries for future portable, and electric-vehicle, applications.